The present invention relates to a run-up control for the pressure cheek of a drawing apparatus in a press.
In transfer presses, multi-stage presses, composite press installations and similar forming presses, for increasing the timing rates, it is required that the formed sheet metal parts be gripped by the transfer device immediately after the opening of the tool and thus before reaching the starting height of the pressure cheek. For this purpose, the upward movement of the pressure cheek must be interrupted.
German Patent Document DE 40 32 338 A1 describes a drawing apparatus of a drawing stage in a press which has a pressure cheek for holding the metal sheet during the drawing. The pressure cheek can be acted upon from below by pressure cylinders. Locking cylinders are provided for an intermediate stop when the workpieces are moved upward. For this purpose, the piston rods are applied to a liftable and lowerable console which all pressure rods have in common. Locking cylinders act upon the console, the pistons of which can be controlled away for a continued upward movement of the pressure cheek.
European Patent Document EP 0 151 198 B1 shows a press control which has a pressure control device. The press control generates signals guided on amplifier units for the basic pressure adjustments as a function of the tool and for the pressure adjustments during the operation of the press.
An object of the present invention is to provide a press in which the tool-specific most favorable removal heights are adjustable during the stoppage of the pressure cheek in the run-up phase and the removal height to be adjusted can be achieved by a control also in the case of varying drawing apparatus pressures.
This and other objects are achieved by the present invention which provides a run-up control for a pressure cheek in a drawing apparatus of a press, comprising a first piston rod with a pressure piston with an effective surface which can be acted upon in a drawing direction, the first piston rod being operatively connected with the pressure cheek. A press control adjusts pressure. A control cylinder having first and second pressure spaces and a second piston rod with a control piston that separates the first and second pressure spaces is provided. The main pressure space is in a constant flow connection with the first pressure space, and the second piston rod extends out of the control cylinder. A pressure generator and a pilot valve controlled by the press control are also provided. The second pressure space is flow connected to the pressure generator via the pilot valve. An actuating drive is coupled to the press control. An adjustable stop is operatively connected to the actuating drive so as to be adjustable in a longitudinal dimension of the second piston rod. A fixed stop is coupled to the second piston rod, the fixed stop abutting against the adjustable stop when the second pressure space is pressurized via the pilot valve.
In the individual case, the pre-acceleration cylinder for the run-up control, which exists in any event, can be used in an advantageous manner, in that the fluid amount displaced from the pre-acceleration cylinder under the pressure of the drawing apparatus after the forming displaces a control piston which can be controlled in its yielding movement.
Another advantage is the adjusting possibility of a volume compensation via the stop adjustment as a function of the different drawing pressure after, for example, each tool change. Furthermore, for a stoppage time of the drawing apparatus, in the lower dead center, a pressure compensation may take place as a function of the pressure in the drawing apparatus.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.